MATLAB: How to get the colors of contour plot after MATLAB R2014b

cdatacmapcolormaphg2lineMATLABpatch

I have created a "contourf" plot, and because of limitations with the "contour" functions, I would like to get the contour data and replot it using other functions.

Before R2014b, contour plots had "patch" objects that I could access. I could get the "CData" from each layer of the contour plot. With HG2, charting objects no longer use patches. How do I recreate get the contour plot's color data?

Best Answer

These are the steps that you can follow to accomplish your workflow after R2014b:

1. Create a contour plot with your data and save the contour matrix in a variable.

2. Parse the contour matrix to save all the vertices in each contour level. Concatenate all the contours for a given level into one vector, with breaks delimited by NaN, and a NaN at the end of the vector.

3. Plot each vector as a patch and just show the edges. Please note that the advantage of using “patch” over “plot” is that you can set the “CData” for each patch (one per level) to that level’s value. If you used the "flat" option for "LineColor" in your contour plot, you can use the "flat" option for "EdgeColor" in the "patch" properties and recreate the color scheme.

You cannot use the "plot" function to recreate a contour plot because they create "line" objects, which do not use the colormap.

Please refer to the “patch” and “contour” properties pages at these links for more information:

https://www.mathworks.com/help/releases/R2015b/matlab/ref/patch-properties.html

https://www.mathworks.com/help/releases/R2015b/matlab/ref/contour-properties.html

Related Solutions

MATLAB: How to add 3D labeled contours to a surface plot

The functions 'surf', 'contour3', and 'clabel' can be used together to produce an elegant plot. The example below demonstrates how:

>> figureHandle = figure;
>> axesHandle = axes(figureHandle);
>> hold on
>> surfaceHandle = surf(axesHandle, peaks,'linestyle','none','FaceAlpha',0.7);
>> [contourMatrix, contourHandle] = contour3(axesHandle, peaks,'k');
>> hold off
>> clabel(contourMatrix, contourHandle)

MATLAB: Specifying color data for patchm or patchesm

The "cdata" parameter of both the "patchm" and "patchesm" constructor expects to receive a singular color value, specified as either a color name (e.g. 'r' or 'red') or an RGB triplet (e.g. [1 0 0]). It will not take in a vector of color values that correspond to the different face colors.

Unlike "patch", providing a scalar value for "cdata" in the constructor for "patchm" or "patchesm" does not use the "CDataMapping" property to map into the colormap.

However, since "patchm" supports nearly all the properties that are supported by the "patch" function, we can color the faces by passing property name/property value pairs to the "patchm" function, as follows:

>> patchm(latData, lonData, 'FaceVertexCData', faceColors, 'FaceColor', 'flat')

This command will create a single patch with multiple faces, with the face colors specified by the array "faceColors". Specifics on the allowed formats of the array "faceColors" can be found on the Patch Properties documentation page, under the property "FaceVertexCData", linked here:

https://www.mathworks.com/help/matlab/ref/matlab.graphics.primitive.patch-properties.html

Since "patchesm" returns an array containing a separate patch object for each face, it is necessary to set the color of each of the patch objects individually to accomplish the same behavior.

For more information about these properties, please refer to the above link.

Best Answer

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MATLAB: How to add 3D labeled contours to a surface plot

MATLAB: Specifying color data for patchm or patchesm

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